This invention relates to plastic bags and, more particularly, to gussetted bags, especially bags commonly referred to as T-shirt bags.
A bag commonly in use throughout the United States and elsewhere is known as a T-shirt bag. T-shirt bags are customarily made from tubular plastic film which is gussetted, sealed and cut to form a bag with handles on the sides of the bag.
The handles for a T-shirt bag are formed from the gussetted side regions. As a result, when the bag is loaded and lifted by the handles, relatively large forces are applied in opposite direction to the areas at the junctions of the bottom seal and the gusset folds. The bag, therefore, is most likely to tear at those junctions when it is loaded and lifted by the handles.
If an overloaded bag does not rupture at the gusset-bottom seal junctions, it is likely to tear at the handles. The handles can be strengthened if they are made wider, but the width of the handles is limited to the width of the gussets, and the wider the gussets the weaker the junctions of the gussets and the bottom seal.
To overcome these problems, the thickness of the plastic film can be increased or the quality of the plastic can be improved but the junctions, while strengthened proportionately, will remain the weakest areas in the bag. These solutions, moreover, result in added expense by virtue of the increase in quality or quantity of the raw material.
Furthermore, when the tubular film is gussetted, the thickness of the gussetted regions at the sides of the bag is twice that of the ungussetted portion in the center. The sealing means which forms the seal at the bottom of the bag must provide sufficient heat to weld together all four layers in the gussetted regions. This is more heat than is required for the ungussetted central region of the bag. The excessive heat applied to the ungussetted portion creates a weakness, particularly in the area of the junctions of the gusset folds and the bottom seal.
One possible approach to this problem is to increase the sealing time by decreasing the speed of the sealing process. This change, however, does not totally solve the problem and, moreover, because of the decrease in production speed, results in increased costs for the final product.
The principal object of this invention is to provide a gussetted plastic bag which is stronger than prior art bags of comparable construction and which is essentially no more expensive to make.
Another object of the invention is to provide a gussetted plastic bag in which the junctions of the gusset folds and seal line are not the weakest areas of the bag.
A more specific object of the invention is to provide an economic way of strengthening a conventional T-shirt bag without significantly increasing the cost of manufacture.
A still further object of the invention is to provide a T-shirt bag having wider handles for a given thickness of plastic film.
In accordance with the invention, at least one plastic tape is bonded to the bottom of a gussetted plastic bag over a region which includes, or is close to, the junctions between the gusset folds and the bottom seal. Preferably, two tapes are applied to opposite sides of the bag or a single plastic tape is folded across the seal. The effect is to transfer the forces normally applied to the seal/gusset junctions to the tape so that the bag will no longer tear first in the areas of the two junctions.